Add --with-system-zlib in bfd

Add --with-system-zlib in bfd

This patch adds --with-system-zlib and remove --with-zlib in bfd.

	* Makefile.am (ZLIB): New.
	(ZLIBINC): Likewise.
	(AM_CFLAGS): Add $(ZLIBINC).
	(libbfd_la_LIBADD): Add $(ZLIB).
	* compress.c: Don't check HAVE_ZLIB_H to include <zlib.h>.
	(decompress_contents): Don't check HAVE_ZLIB_H.
	(decompress_contents): Likewise.
	(bfd_compress_section_contents): Likewise.
	(bfd_get_full_section_contents): Likewise.
	(bfd_init_section_decompress_status): Likewise.
	(bfd_init_section_compress_status): Likewise.
	* configure.ac (AM_ZLIB): Removed
	(zlibdir): New.  AC_SUBST.
	(zlibinc): Likewise.
	Add --with-system-zlib.
	* Makefile.in: Regenerated.
	* acinclude.m4: Likewise.
	* config.in: Likewise.
	* configure: Likewise.
	* doc/Makefile.in: Likewise.